'Artificial blood cells' could heal surfaces

A computer simulation shows a 10-micron-wide capsule moving across a surface

(Image: Anna Balazs)

Microscopic polymer capsules could someday heal surfaces by filling in damage in a similar way to blood cells inside the human body, according to sophisticated computer models.

The simulations show that microcapsules, travelling across a surface within the flow of a liquid, should naturally cluster around points of damage. Nanoparticles that leak out of the capsules should then fill the breach. Once the damage has been repaired, capsules could start flowing over the surface once again.

“We know how to make everything involved in this set up,” says Anna Balazs at Pittsburgh University in the US. “We used our models to make a kind of recipe for experimentalists so they could fabricate it.”

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In Balazs’s computer models, microcapsules measuring tens of microns in diameter would roll across the surface of a channel carried by a liquid. Both the microcapsules and the surface would be coated in a hydrophobic (water-repellent) substance, allowing the capsules to roll over the surface.

Worn away

Any damage sustained inside the channel would also remove the wall’s hydrophobic coating. When the microcapsules reach this point, the effect that allows them to roll along is removed. “If the wall’s coating is worn away or ruptured the material below is exposed,” Balazs told New Scientist. “The microcapsules will stop because they can’t move onto that surface.”

Balazs likens the microcapsules’ action to that of blood cells in the human body. Nanoparticles inside the capsules would leak out capsules at a steady rate, and should therefore be concentrated at the site of damage, providing they reach it quickly enough. “Those particles can heal the break and recreate a surface that lets the microcapsules flow once more,” Balazs adds.

She says this could be useful in micro-fluidic chips, which use tiny channels to route small amounts of liquid around for analysis. Microcapsules added to the liquid flowing through a chip could extend its lifetime by healing any worn patches inside, Balazs says.

Big cracks

“You’re not going to seal big cracks like this,” says Ian Bond, an expert on self-healing materials at Bristol University in the UK (see Spacecraft skin ‘heals’ itself).

Bond notes that optical materials rely on surface properties to manipulate light. The microcapsules “could be useful” for keeping these surface coatings intact, he says.

“Soldiers in Iraq have to throw away their goggles quite often because the coating gets rubbed off by sand,” he explains. “Perhaps they could be healed by immersing in a flow of microcapsules at the end of the day.”